- Hormones can be classified based on their chemical structure, including peptide/protein hormones, steroid hormones, and amino acid derivatives. - Oxytocin is a peptide hormone (specifically, a nonapeptide). - Corticotropin (ACTH) is a peptide hormone (a polypeptide of 39 amino acids). - Insulin is a protein hormone composed of two polypeptide chains linked by disulfide bonds. - Cortisone is a steroid hormone, derived from cholesterol.